To investigate the role of experience in interspecific emotion perception, humans with various levels of dog experience provided their interpretations of emotion in dogs using the dogs' visual signals (body language). First, a set of 30 short videos of dogs was assembled, and a panel of eight behavioral experts provided ratings and categorizations of the depicted dogs' emotions. Based on the emotional valence and level of agreement in their ratings, a subset of 16 videos was selected for inclusion in a web survey made available to the general public. The wide range of dog experience found within the final sample of 2,163 participants allowed for various means of assessing the effect of experience on interspecific emotion perception. Responses were analyzed according to broad experience categories (never owned a dog, dog owner, dog professional for less than ten years, dog professional for ten or more years), as well as experience-related variables among the dog owners. Effects on emotion perception were found using all experience-related measures. The level of experience with dogs predicted both ratings and categorizations of emotion in dogs. The role of experience was more evident for emotional displays that had been judged by experts to be clearly negative than clearly positive. Less-experienced individuals tended to provide more positive emotion ratings of negatively-valenced behavior than more-experienced individuals. In addition, they were more likely to diverge from expert evaluations and categorize such behavior as happy, rather than fearful. Furthermore, as previous education about dog body language increased among more-experienced individuals, perceptions became more aligned with expert evaluations, while perceptions of individuals who had never owned a dog became less aligned. Lastly, differences among the experience groups in emotion ratings and categorizations were reflected in differences in observational focus. Individuals with greater experience were more likely to attend to the ears of the dog and less likely to attend to the legs and tail. In sum, individual differences in dog experience were associated with the perception of emotion in dogs, suggesting experience-dependent development of these abilities. These findings are among the first to provide evidence for experience-associated variation in interspecific emotion perception and may illustrate a novel strategy for exploring the development of individual differences in emotion perception in humans.